FIG. 38 shows a conventional exterior view inspecting apparatus for circuit board.
A displacement sensor 11 detects the existence and position of an electronic component on a circuit board. An X-axis robot 25 and a Y-axis robot 27 moves the displacement sensor 11. A pair of conveyors 30 disposed parallel convey a circuit board 4. A sensor 35 detects the arrival of the circuit board 4. A fixer 40 fixes the circuit board 4 so that it may not move during inspection. A controller 2 is connected through a signal cable 8, and controls this apparatus.
As shown in FIG. 39, the X-axis robot 25 and Y-axis robot 27 move the displacement sensor 11 according to the position data of an electronic component 5 stored in the controller 2.
The displacement sensor 11 scans the circuit board 4 along the route containing the electronic component 5, once in the X- or Y-direction with a laser beam.
By this scanning, the change in distance between the displacement sensor 11 and the circuit board 4 on which the electronic component 5 is mounted, which is called a displacement hereinafter, is detected
FIG. 40(a) shows a trace 300 of the laser beam emitted by the displacement sensor 11.
FIG. 40(b) is a waveform of displacement detected by the displacement sensor 11, and level Ha denotes the circuit board 4, and level Hb shows the electronic component 5. By a threshold value 301 set between level Ha and level Hb, both ends L1 and L2 of the electronic component 5 are detected.
The exterior view inspecting apparatus for circuit board judges the existence of the electronic component 5 if both L1 and L2 are present, and judges the absence of the electronic component 5 if neither L1 nor L2 is present.
Furthermore, the exterior view inspecting apparatus for circuit board judges that the electronic component 5 is at a correct position if both L1 and L2 are in a predetermined area, and judges that the electronic component 5 is at a wrong position if L1 and/or L2 is outside the predetermined area.
The conventional exterior view inspecting apparatus for circuit board, however, does not detect the deviation of position of the electronic component 5 indicated by broken line 5a or 5b in FIG. 40(a) because L1 and L2 in this case cannot be distinguished from the correct position of L1 and L2 of the electronic component 5 indicated by solid line.
This problem may be solved by increasing the number of scannings by the displacement sensor 11, but it requires starting and stopping of the X-axis robot and Y-axis robot on every scanning, and it gives rise to a new problem of necessity of a long time for inspection, which is not preferable.
The invention hence presents an exterior view inspecting apparatus for circuit board capable of detecting the position of an electronic component on a circuit board accurately and in a short time.